The summit's Irish founder, Paddy Cosgrave, on Wednesday announced he would "rescind Marine Le Pen’s invitation" on Wednesday, even though he had earlier defended her inclusion despite her "wrongheaded" views.
"Attempting to ignore these views, which have been fanned in our view by technology, does little to furthering understanding," he argued initially.
It’s clear to me now that the correct decision for @WebSummit is to rescind Marine Le Pen’s invitation.Paddy Cosgrave (@paddycosgrave) 15 août 2018
Standing on an anti-immigrant, Europhobic programme, Le Pen won 34 percent of the votes in the second round of France's presidential election last year.
Since then her National Front has changed its name to National Rally but not its policies.
Citing a "large reaction online overnight", Cosgrave on Wednesday tweeted that the invitation was "disrespectful in particular to our host country" and to "some of the many tens of thousands of attendees who join us from around the world".
Portugal was ruled by a right-wing dictatorship for 41 years until it was toppled in the 1974 Carnation Revolution.
The Le Pen invitation sparked outrage in Portugal, particularly on the left.
On Tuesday the Left Bloc, a hard-left alliance allied to the ruling Socialists, called on the city council of Lisbon, where the conference is to take place in November, and the government to take a stand on the question, accusing Le Pen of inciting "hatred, xenophobia and racism".
Cosgrove said then that he would abide by the government's decision but it declined to take a stance.
Some Socialist Party members, however, opposed "giving a platform to fascism" and the row spread to social media.
Moved from Dublin
The first Web Summit was held in Dublin in 2009.
It moved to Portugal in 2016, following a row with the Irish government over facilities and infrastructure.
It expects 70,000 people to attend this year and has invited some 1,000 speakers.